Recently, a pressure on an increase in energy capacity is intensified so as to increase a fuel ratio of an electric vehicle (generally, including a hybrid car, a plug-in hybrid car, an electric car, and the like). However, an increase in capacity of unit battery cells is limited due to a limitation of capacity of a battery pack in terms of a process technology and a cell technology. For this reason, the energy of the battery pack is increased by arranging a predetermined unit battery cells in a serial and parallel structure.
In addition, in order to minimize tolerance current in a vehicle such as an electric bus, and the like, a high-voltage (about 700 V) motor is being developed. Therefore, the number of unit battery cells connected with each other in series has been very increased (for example, connecting 180 serial cells with each other in about 100 cells connected with each other in series). The pack parallel structure for increasing the number of serial unit battery cells and the energy capacity has a great effect on a technology of a battery management system (BMS) that transmits battery information to a vehicle controller within the electric vehicle. In particular, the increase in the number of unit battery cells causes problems such as an increase in weight and volume of wiring harness for sensing voltage, a reinforce of BMS internal voltage due to the formation of high voltage end, and the like.
In particular, since a battery status information calculation such as a state of charge (SOC) of a battery using the cell voltage value of the existing about 100 cells is calculated by receiving information of 180 cells, an error in a calculation may frequently occur.
The reason is that in the battery pack in which a plurality of serial unit battery cells are connected with each other in series, the wiring harness of voltage and temperature is connected to one sub BMS and each of the sub BMSs measures a current value flowing in each of the corresponding sub packs.
Further, the measured voltage, temperature, and current are used to calculate the state of charge (SOC), the tolerance current, or power of the battery, battery cooling, cell balancing, battery diagnosis information are calculated by a control unit of the sub BMS.
Further, each sub BMS transfers the calculated information and characteristic values among the measured values to a main BMS and the main BMS calculates and transfers the information to be transmitted to the vehicle controller using the corresponding sub BMS value as the information.
The voltage sensing number between the sub-pack and the sub BMS calculates each battery information in the sub BMS based on more than 100 voltage sensing wires, more than 10 temperature sensing wires, and data collected by each current sensing once.
Therefore, as the number of serial unit battery cells is increased, the wiring harness of the cell voltage and the battery temperature is long and thick and as a result, has a very vulnerable structure to the operation of the vehicle. Therefore, it is highly likely to cause malfunction and firing of a system during driving.
Further, the sub BMS is attached to the sub pack one by one and therefore, costs are greatly increased. In particular, for cell voltage of 100 cells or more, high-voltage elements need to be used and therefore, costs are greatly increased.